1. Field of the Invention
This invention relates to a vertical heat exchanger and a method for the use of the heat exchanger.
2. Description of the Related Art
FIG. 1 is a cross section of the general shell-and-tube heat exchanger. Heretofore, it has been customary for a vent pipe 6 to be mounted on the shell, as illustrated in FIG. 1, below an upper tube sheet 8 of a heat exchanger 1 because it is welded as by using a reinforcing ring for the purpose of making up the strength of an opening part thereof and is inevitably required to have a certain distance from the tube sheet. In such a vertical heat exchanger, a high-temperature fluid such as liquid is introduced from a tube side fluid passing port 2 and drawn out from another tube side fluid passing port 3, and conversely a low-temperature fluid such as liquid is introduced from a shell side fluid passing port 4 and drawn out from another shell side passing port 5. In this case, the vent pipe 6 and a drain pipe 7 are not connected to a pipeline. At the time of start, the drain pipe 7 is closed, the vent pipe 6 opened to expel the entrapped gas from the shell, and then during the course of normal operation the drain pipe 7 and vent pipe 6 are both closed.
In this method, however, a gas portion occurs between the vent pipe 6 and the upper tube sheet 8, with the result that a heat-transmission area will be decreased and a thermal efficiency will be lowered in this part of the exchanger. In addition, this gas portion in the gas-liquid phase boundary sometimes induces corrosion of the inner part of the exchanger and the outer part of the tubes.
When the operation of the shell-and-tube heat exchanger is stopped, the drain pipe 7 is utilized to discharge sludge or liquid collected in the shell. This drain pipe 7 is however welded as by using a reinforcing ring adapted for making up the strength of an opening part of the shell and is required to have the allowance of a certain distance from the tube sheet, i.e., the drain pipe 7 is disposed at a level higher than a lower tube sheet 9, so that the sludge accumulated in the part lower than the drain pipe 7 cannot be discharged. In the bottom part of the heat exchanger, sludge is constantly accumulated or part of liquids remains.
Spiral heat exchangers also entail the same problem as the shell-and-tube heat exchangers.